Muffler with reed valve providing continuous venting

ABSTRACT

A muffling technique wherein a cantilever-supported spring reed normally blocks a major portion of an exhaust outlet opening while a minor portion of the exhaust outlet opening continuously vents an amount of exhaust gas sufficient to avoid substantial flutter of the reed during engine idle and to avoid substantial floating during engine operation.

atent Bailey 14 1 Feb. 22, 1972 [54] MUFFLER WITH REED VALVE [56] References Cited PROVIDING CONTHNUOUS VENTING UNITED STATES PATENTS 72 I t h B I l Jay aney wwdland Calf 3,129,784 4/1964 Smallpeice 1181/64 B [73] Assignee: McCulloch Corporation, Los Angeles, 3,132,716 5/1964 Williams ..18l/64 A Calif. 3,318,412 5/1967 Bailey 181/65 [22] Flled: 1970 Primary Examiner-Robert S. Ward, Jr. [21] Appl.No.: 101,572 Attorney-Bums,Doane,Swecker&Mathis [57] ABSTRACT [52] U.S.Cl ..181/40, 181/64 B, 181/65, A muffling technique wherein a cantilever-supported spring 181/36 R reed normally blocks a major portion of an exhaust outlet [51] llnt. Cl ..F01n 7/10, FOln 1/22, FOln 3/06 opening while a minor portion of the exhaust outlet opening [58] Field of Search ..l8l/64, 64164.2, 65,49, continuously vents an amount of exhaust gas sufficient to 181/40, 36 R, 36.1, 72 avoid substantial flutter of the reed during engine idle and to avoid substantial floating during engine operation.

21 Claims, 12 Drawing Figures "19 1 l I l I 4'] l-l--- -l Q PAIENIEBFEB22 m2 SHEET 2 [1F 3 FIG. 2

00 oo oo oo 0 00 oo oo MUFFLER WHTH REED VALVE PROVllDlNG CONTINUOUS VENTHNG BACKGROUND OF THE INVENTION This invention relates to mufflers. In particular this invention relates to mufflers for internal combustion engines of the type utilized to provide a drive for chain saws.

In the US. Bailey Pat. No. 3,3l8,4l2, assigned to the as signee of the present invention, there is disclosed a muffler including a thin, cantilevered metal reed extending over a circular'exhaust opening of the muffler. The disclosed arrangement functions to reduce the noise level which would otherwise be present in connection with the operation of an internal combustion engine, for example, an engine of the type encountered in chain saw combinations.

As pointed out in the disclosure of the Bailey patent, the sound level of two-cycle engines is high over a broad band of frequencies so that even the noise in the low-frequency bands must be attenuated. Moreover, sound waves emitted from such an engine are trains of discrete sharp-fronted pressure pulses. The introduction of the reed into the exhaust stream tends to smooth out the sharp-fronted pressure pulses and spread the noise energy over a longer period. In operation, high intermittent pulses of short wave duration are reacted by the inertia and spring force of the reed and the reed is operative to return energy to the exhaust stream.

Arrangements of the type set forth in the aforementioned Bailey patent have constituted a significant advance when compared with traditional prior approaches. Nevertheless, it has been found that two operational phenomena may be amenable to improvement. The first of these phenomena involves the flutter or clatter of the reed which may be encountered during engine idle. As pointed out in the aforementioned Bailey patent, the reed dimensions to be employed in the disclosed muffler are such that the resonant frequency is above the highest exhaust pulse frequency of the engine and the reed stiffness is as low as possible in order to avoid excessive back pressure. With these conditions being met, the action of exhaust gases on the reed during engine idle condition may sometimes produce a clattering noise attributable to flutter of the cantilevered reed reacting to the idle exhaust.

It would be particularly desirable to avoid substantial flutter of this type while retaining many of the advantages of the reed muffler of the type set forth in the Bailey patent. Particularly, it would be desirable to avoid substantial reed flutter during engine idle without utilization of a reed that would undesirably produce a back pressure resulting in significant horsepower loss.

A further operational phenomena, the avoidance of which would be desirable from a reduced noise level standpoint, involves reed floating," i.e., the tendency 'of the reed to stay open during engine operation. Such floating results in a noise level greater than that which would be encountered were the reed to open and close regularly with each exhaust pulse. Moreover, operating conditions which result in a floating reed impose somewhat continuous stress conditions on the reed that it would be desirable to eliminate.

It will, therefore, be appreciated that it would be desirable to avoid substantial floating of the reed during engine operation while retaining desirable characteristics of a muffler of the type set forth in the aforementioned Bailey patent.

To this end, the present invention employs a cantilevered metal reed extending over an exhaust opening of the muffler with the reed and the exhaust opening oriented so that in a reed closed position, a major portion of the exhaust outlet is blocked while a minor portion of the exhaust outlet is operative to continuously vent exhaust gases to the surrounding atmosphere. This minor portion of the exhaust outlet is of a magnitude sufficient to avoid substantial flutter of the reed during engine idle and to avoid substantial floating of the reed during the engine operation.

It has been proposed in US. Pat. No. 3,132,716 to utilize a generally circular spring movably mounted on a generally cylindrical mufiler housing and operative to close a curved slot for complete muffling effect or to partially close the same, as desired. The muffler housing is intended to be mounted so as to surround the engine exhaust port. The entire arrangement not only fails to appreciate the floating and flutter phenomena heretofore described, but also contemplates structural relationships that together may not be entirely acceptable for present purposes.

For example, the operational characteristics of the severely curved spring differ substantially from those of the generally elongate and generally flat, metallic reed utilized in the present invention. Moreover, the proposed muffler utilizing the curved spring is intended to be arranged with an engine exhaust port directly aligned with the curved slot with which the spring cooperates. Therefore, exhaust may pass directly from this exhaust port to the spring so that the possibility of flutter and floating problems may be greatly enhanced.

It will also be apparent that since the circular spring is detented in position, the possibility of displacing the spring during operation and thereby changing muffler characteristics is present. Such displacement may also be coupled with interference with muffling action caused by a ledge intended to closelybound the curved detented spring, These facts are of particular significance where mufflers are utilized in combination with chain saws involving multidirectional vibrational characteristics when the chain saw is in use.

Moreover, from an accessibility standpoint, the prior proposed assembly may not be particularly advantageous in the provision of a muffler housing that surrounds rather than abuts an engine exhaust port.

It has also been proposed in German (Karthaus) Pat. No. 290,089 to utilize a muffler wherein exhaust gases are guided through a narrow slit extending over the entire length of a muffler housing, with the slit being covered up by a steel band that can be easily bent upwards. The band is to be attached to the muffler housing by screws. It will be appreciated that the exhaust flow characteristics through the narrow slit, which is coextensive with the mufiler housing length, may not be entirely acceptable.

Moreover, this prior proposed arrangement does not involve a cantilever supported, resilient spring-type reed. As such the ability, if any, of such an arrangement to smooth out the sharp-fronted pressure pulses, such as those associated with two-cycle engines, might be insignificant. At any rate, adequate design of the steel band, anchored along its length, so as to account for both resonant frequency and stiffness considerations, might prove troublesome.

A muffler including a pivotable and inclined tongue within a confined exhaust passage and biased by a spring, at one end, toward a position wherein the passage may freely communicate with the surrounding medium, has also been proposed in German (Pieron) Pat. No. 814,969. The need for a separate spring element in such an arrangement is not entirely desirable.

Additionally, the tongue performs little or no diffraction function externally of the muffler housing, and such a function may be acoustically desirable. It is also of significance that since the movable tongue is in a confined exhaust passage, the exhaust flow characteristics may be undesirably irregular within the confined passage.

Considerations other than those noted above will be recognized as dictating the desirability of providing a simple structure that retains many of the advantages of the arrangement disclosed in the aforementioned Bailey patent while minimizing problems associated with flutter and floating.

OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, a general object of the present invention to obviate or minimize the disadvantages of the sort previously noted.

It is a particular object of the invention to provide a novel muffler employing a cantilevered metal reed wherein substantial flutter of the reed during engine idle and substantial floating of the reed during engine operation are avoided.

It is a further object of the invention to provide such a muffler in combination with a chain saw driven by internal combustion engine wherein the multidirectional vibrational forces encountered during chain saw operation will not dislodge the reed.

It is still a further object of the present invention to provide such a novel muffler wherein the exhaust inlet of the muffler and the exhaust outlet of the muffler are operationally displaced from alignment with one another to avoid direct impact on the reed valve of exhaust gases entering the muffler housing.

It is still another object of the present invention to provide such a novel muffler wherein a spark arrestor may be included in a readily replaceable position.

It is yet another object of the present invention to provide a novel reed muffler retaining advantages of the muffler disclosed in the aforementioned Bailey patent and additionally structured to militate against flutter and floating problems.

It is yet another object to provide a novel reed muffler combination with novel relationships of the adjacent reed and exhaust port configurations.

It is still another object of the present invention to provide a novel chain saw and muffler combination.

It is still a further object of the present invention to provide a novel muffling method that militates against substantial floating and flutter of a cantilevered reed.

SUMMARY OF PREFERRED EMBODIMENTS OF THE INVENTION Preferred embodiments of the invention intended to accomplish at least some of the foregoing objects entail the provision of a chain saw having an internal combustion engine with a muffler housing defining an exhaust gas flow path, preferably in the form of an expansion chamber. The expansion chamber has an exhaust inlet communicating with the engine exhaust port, and an exhaust outlet opening communicating with the surrounding atmosphere. The inlet and outlet may be disposed operationally out of alignment to define a somewhat tortuous exhaust gas flow path.

Preferably, the engine displacement is in the range of about 2 to 8 cubic inches and the exhaust outlet opening has an effective area in the range of about 0.25 to 1.25 square inches.

A flexible, elongate reed spring having a length dimension greater than its width dimension, is supported in cantilever suspension externally of the housing with the spring being anchored adjacent one longitudinal end thereof. The other end of the spring is disposed so as to normally block, in a reed closed position, a major portion of the muffler exhaust outlet. The remainder of the area of that outlet opening provides continuous venting communication between the exhaust gas flow path and the atmosphere surrounding the housing. Preferably, the venting or unblocked portion of the exhaust outlet is com prised of an area in the range of about to 45 percent of the total outlet area, i.e., the blocked portion compresses about 55 to 85 percent of the total.

The reed is deflectable to a reed open position in response to exhaust gases passing through the exhaust gas outlet. It is preferred that the exhaust gas pressure be in a range of about I to 10 psi and that the force required to deflect the reed to an open position is in range of about I to 10 pounds.

In some preferred configurations the elongate spring reed is generally flat and is supported on a generally flat planar surface which may be on the external portion of the rigid muffler housing.

The minor portion of the exhaust outlet is designed to be of a magnitude that will continuously vent an amount ofexhaust gas sufficient to avoid substantial flutter of the reed during engine idle and to avoid substantial floating of the reed during engine operation. It is generally preferred that the venting flow path be bounded, at least partly, by a generally curved peripheral boundary. For this purpose the exhaust outlet opening may be provided in a generally circular configuration. ln any event, the reed and the exhaust outlet opening cooperate to define the venting flow path and the reed may define a portion of the generally curved peripheral boundary.

In one preferred embodiment the end of the reed remote from its anchor is provided with at least one aperture disposed over the exhaust outlet opening and generally concentric therewith in a reed closed position. In another embodiment the generally circular exhaust outlet opening is defined by a scalloped periphery and the curved peripheral boundary of the venting flow path is provided by portions of that periphery not blocked by the reed. In a further embodiment, a radiused tip reed cooperates with corners of a quadrilateral or triangular shaped exhaust outlet.

For some purposes the reed spring may be provided with a generally straight terminus. Such an embodiment may facilitate insertion and removal of a cup-shaped spark arrestor seated in the exhaust outlet and extending into the muffler housing. It will, however, be appreciated that a generally curved spring terminus may be employed.

If desired, a. straight terminus reed may include an edge extending not only generally transversely of but also inclined with respect to the longitudinal extent of the reed spring. With such a configuration, direction of the exhaust downwardly and away from the user of the chain saw may be accomplished as will hereinafter become apparent.

A method aspect of the invention entails the venting of exhaust gases through a minor portion of the muffler outlet opening during engine idle and during engine operation respectively to prevent substantial flutter and floating of the cantilever supported reed.

Other objects and advantages of the present invention will become apparent from the following detailed description of preferred embodiments thereof with reference to the accompanying drawings in which like numerals refer to similar elements and in which:

THE DRAWINGS FIGS. I and 2 are each fragmentary elevational views of a chain saw embodying the present invention;

FIG. 3, is a plan view of the muffler shown in FIG. 1 taken along line 33 therein;

FIG. 4, is a transverse sectional view taken along line 44 of FIG. 3 and partially illustrating the relationship between the muffler and engine of FIG. 1;

FIGS, is a view taken along line 55 of FIG. 2 and partially illustrating the relationship between the muffler and engine of FIG. 2;

FIG. 6, is a partial plan view similar to FIG. 3 but with the reed stop removed;

FIGS. '7, 8 and 9, are partial plan views similar to FIG. 2 but illustrating other embodiments of reed mufflers according to the present invention with the reed stop broken away;

FIGS. 10 and II, are plan .views of reeds respectively utilized in the embodiments of FIGS. 7 and 8.

FIG. 12, is a plan view similar to FIG. 2 and illustrating another embodiment of the invention.

DETAILED DESCRIPTION With reference to FIGS. I and 2, the overall structure of a chain saw 10 embodying the present invention may be seen. These two FIGS. 1 and 2 differ primarily by the orientation of the muffler employed in the combination. The chain saw includes a-guide bar 12 supporting a cutter chain I4. A triggertype, throttle lever 16 may be provided on a handle 18. A twocycle internal combustion engine 19 serves to impart power to the cutter chain M thereby causing the chain 14 to traverse the periphery of the guide bar 12.

A suitable drive connection 20 is interposed between the engine 19 and the cutter chain 14. This drive connection 20 may include a conventional pull starter 22. It will, however, be

appreciated that an electrical self-starting system may be provided.

The structure thus far described is itself well known in the chain saw art and is generally of the type disclosed in U.S. Pat. No. 3,498,280, assigned to the assignee of the present invention. When the chain saw it) is in use, it exhibits multidirectional vibration characteristics.

A reed muffler 24 is carried by the chain saw cutter 10. Although several muffler embodiments are illustrated and described in detail hereinafter, it will be appreciated that basic features of the different embodiments are interchangeable particularly in connection with the hereinafter discussed reed stops and reeds. Moreover, it will become apparent that reed mufflers 24% with features of the several embodiments can be employed in the orientation of either FIG. )1 or FIG. 2, as well as in other orientations.

With reference to FIGS. 3 and 4, the orientation of the muffler 24 with respect to a cylinder of the engine 19 of FIG. ll will be appreciated. FIG. 5 illustrates the orientation of the muffler 24 with respect to the cylinder of the engine 19 of FIG. 2.

The muffler 24 of the present invention includes a rigid housing 27 defining an exhaust gas flow path, which in the case of the illustrated embodiments constitutes an expansion chamber 28. The housing 27 includes an exhaust inlet 29 and an exhaust outlet 30. The exhaust inlet 29 and the exhaust outlet 30 are preferably operationally displaced from alignment with one another so that exhaust gases passing through the muffler follow a relatively tortuous path, i.e., the stream of exhaust gas passing from an exhaust port of the engine cylinder does not directly impinge upon the reed 32 extending over the exhaust opening 30.

The muffler housing 27 for mufflers to be used in the orientation of FIG. 1 includes a generally rectangular hollow bottom portion 34 which telescopingly receives a top portion 36 in which the inlet and outlet openings 29 and 30 are provided. The two housing portions 3 t and 36 may, if desired, be suitably brazed together at their juxtaposed peripheries along a seam indicated at 38. Crimping or spot welding may alternatively be performed to unitize those housing portions. Internally of the housing portions, the expansion chamber 28 is provided.

A raised ledge section 40 is included along one side of the upper housing portion 36. This ledge section 40 is provided with an opening that communicates with the exhaust inlet 29.

The exhaust inlet 29 may have a generally oblong configuration as illustrated, and may be defined in a generally flat adapter member 42 seated on the ledge portion 40. This adapter member 42 may be suitably secured to the ledge portion by brazing or the like. It will be appreciated that the adapter member presents a flat surface 44 that may be abutted against the cylinder of the engine 19 with the exhaust inlet 29 aligned with the exhaust port of that cylinder.

Suitable aligned apertures are respectfully provided in the adapter member 412 and the bottom wall of the lower housing portion 34. These apertures serve to receive suitable fasteners 45 for securing the muffler in position on the cylinder. A further such fastener 45 may be provided on the opposite side of the muffler for securing the muffler to a suitable projection (not shown) from the cylinder block.

The external periphery of the upper wall of the upper housing member 36 includes a generally flat surface 46 laterally offset from and spaced below the raised ledge 40. As illustrated, the flat surface 4 6 is inclined with respect to plane of the seamed intersection 38 of the upper and lower housing portion.

During operation of the muffler, maximum deflection of the reed 32 will occur at the end thereof projecting beyond the cylinder. This projection is best viewed in FIG. 4. The inclina tion of the flat housing portion 46 enables a compact positioning of the muffler as shown in FIG. 1 without cylinder interference with the reed and its associated stop 47, hereinafter more fully described.

At the end of the flat portion 46 adjacent the free end of the reed 32, the exhaust opening 30 of the muffler is provided. As illustrated, this opening 30 may be generally circular in configuration and may be provided by a stamping that results in a downturned annular flange 48 extending inwardly of the housing 27. By reason of the outwardly flared surface 50 at the intersection of the flange 48 with the outer flat surface do, the actual or effective exhaust port area slightly exceeds the area encompassed by the flange.

Beneath the flat surface 46, and secured to the upper housing portion 36 internally of the expansion chamber in any suitable manner, is a mounting block 52. This mounting block 52 is provided with threaded apertures 53 aligned with apertures defined adjacent the end of the flat surface as remote from the exhaust outlet 30.

Adjacent one end thereof, a flexible, elongate. and generally flat, thin metallic reed 32 is provided with apertures similarly spaced. The aligned apertures cooperate with suitable securing means such as threaded allen screws 54 to properly position the reed 32.

It will be appreciated that the reed 32 has a length dimension exceeding its width dimension and is cantilever supported by fixedly anchoring the reed externally of the housing 27 adjacent one end of the reed. The major portion of the reed, in a reed-closed position, may be normally supported on the generally flat outer surface 46 of the upper housing portion 36. The end portion of the reed remote from the anchored end, in the reed-closed position, functions to block a major portion of the exhaust outlet 30, while a minor portion of the exhaust outlet 30 is in continuous communication between the expansion chamber 28 and the atmosphere surrounding the muffler housing 27.

With one end of the reed 32 clamped to the flat surface 46, the maximum desirable distance of standoff at the remote reed end (i.e., the amount that the end which is overlying the exhaust outlet should depart from its preferred flat position engaging the flat surface 46 with the reed at rest) is about 0.060 inches. A greater standoff distance might reduce muffling efficiently particularly since continuous exhaust gas venting is involved. With the illustrated arrangement, if a greater than desired standoff is present, the reed may often be turned over to avoid the problem. Thus overdesign of spring force of the reed, which might create back-pressure problems, need not be engaged in merely to insure correct standoff.

During engine operation, i.e., during speeds higher than idle rpm. the reed 32 is deflectable to an open position by the force of exhaust gases passing through the exhaust outlet 30 and acting on the reed to deflect the reed about its anchored end. The exhaust gas pulses thus function to flex the reed 32, with the sharp-fronted pressure pulses being smoothed out and blunted by means of the reed so that the noise energy is spread over a longer period, in a manner similar to that disclosed in the aforementioned Bailey patent. However, the unblocked minor portion of the exhaust outlet is operable to continuously vent an amount of exhaust gas sufficient to avoid substantial flutter of the reed during engine idle and to avoid substantial floating of the reed during engine operation. The reed is preferably designed so that its resonant frequency is above the highest engine exhaust pulse frequency and so that its stiffness is as low as possible in order to avoid excessive back pressure.

The geometrical relationship of the reed 32 and the exhaust outlet opening 30 is best viewed in FIG. 6. The reed 32 so illustrated may be considered to be substantially identical to the reed disclosed in the aforementioned Bailey patent, except that the end of that reed is out off adjacent the outlet opening 30 to expose the previously described minor portion of the exhaust opening. In the muffler embodiment shown in FIG. 6, this exposed minor portion of the exhaust opening takes the form of a segment of a circle bounded by the periphery of the exhaust outlet 30 and the generally straight terminus 32a of the reed 32.

The muffler 24 of FIGS. 2 and S is substantially similar to that already described and includes a housing 27 defining an expansion chamber 28 and exhaust inlet and outlet openings 29 and 30. However, the illustrated housing 27 is shaped generally triangularly in cross section and is disposed in an orientation with the exhaust opening 30 facing laterally of the chain saw 10, i.e., generally normal to the plane of the elongate guide bar l2. Since the housing 27 is disposed laterally of the cylinder of the engine I9, the raised ledge 40 and the inclination of the flat surface 46 on which the reed 32 is seated, in a closed position, may be dispensed with.

It will also be appreciated that the exhaust inlet 29 is suitably disposed at the rear of the mufiler housing 27 and that the housing is suitably attached to the cylinder by screws adjacent the outlet opening 30, as indicated at 45a. These screws 45a may be provided with a suitable nutlike block 45b that bears internally of the muffler to urge it against the cylinder, while the allen heads terminate at the outer muffler portion to facilitate accessibility. A gasket 450 may be additionally pro vided between the muffler and the cylinder.

The bearing block 45b, when the muffler is mounted, may be located in a protrusion of the housing portion 36a defining the inlet opening 29 and adapted to fit in a cutaway portion of fins on the cylinder of the engine 19. Fins otherwise protruding may project to the housing portion 36a for added support.

It will be apparent that the displacement of the inlet opening 29 and the outlet opening 30 (defined in the housing portion 34a) operationally out of alignment is accomplished in the FIG. embodiment by the interposition of a suitable baffling means Sea. In the case of the FIG. 4 embodiment this is accomplished by physical displacement of the openings 29 and 30.

As in the case of the muffler shown in FIG. 6, the reed 32 is provided with a generally straight edge terminus 32b shown in phantom in FIG. 2. However, this terminus 32b is inclined with respect to the longitudinal extent of the reed whereas the straight terminus 32a of the FIG. 6 reed is shown as generally normal to that extent. The inclined terminus arrangement illustrated serves to direct exhaust gases generally forward and downwardly of the user of the chain saw It). A ledgelike portion a of the chain saw body may project laterally beyond the muffler housing as may be seen in FIG. 5. This may aid in deflection of the exhaust gases.

It is thought that suitable results according to embodiments of the present invention may be best obtained by maintaining the blocked portion of the total area of the exhaust outlet opening 30 in the range of about to 45 percent of that total area. Preferably the total area of the exhaust outlet opening is maintained in the range of about 0.25 to 1.25 square inches. These and other preferred parameters thought to be capable of producing suitable results according to the present invention are set forth in the following table:

Range of area ofexhausl outlet opening 025 to 1.25 sq. in.

Range of minor portion of exhaust outlet opening for continuous venting I5 to 45% of total Range of volume of expansion chamber 2 to 40 cubic in. Range of engine displacement 2 to 8 cubic in. Range of ressure ofcxhaust l to I0 p.s.i. Range of force required to flex read I to I0 lbs.

Empirical data wherein a muffler of the type shown in FIGS. 3, 4 and 6 was employed and wherein the muffler included an expansion chamber volume of approximately 3 cubic inches indicated that best results from a noise level standpoint may be obtained, with a 0.785-inch nominal diameter exhaust outlet when the'exposed outlet sector has an area of about 0.084 square inches taking into account the outwardly flaring portion indicated at 50 in FIG. 4 (giving an equivalent radius r of the outlet of about 0.425). In this instance the reed had a width dimension w of about 1 inch and an overall length dimension 1 of about 2%inches, with a cantilever length 0 of about 1% inches. These dimensions r, w, I and c are indicated in FIG. 6, along with the distance s of about 0.250 inch from the center of the exhaust opening 30 to the sector boundary line.

As previously mentioned the reed dimensions were such that its resonant frequency was above the highest pulse frequency of the engine and its stiffness was as low as possible :in order to avoid excessive back pressure. The reed was comprised of Sandvik stainless steel 1 IRS extra hard rolled 18-8 austenitic, 50 percent transformed to martensite heat treated to a Rockwell hardness (R0) of about 5860, with an approxirnate tensile strength of 320,000 to 330,000 p.s.i.

An engine displacement of approximately 3.3 cubic inches was involved; and the area of the muffler inlet opening 29, approximately equal to the engine exhaust port area, was about 0.392 square inches.

A stop 47 such as that shown in FIGS. 3 and 4 was also employed in connection with the reed 32. The stop may include a rigidifying, central longitudinal projection 49 that may be received between fins on the cylinder when the muffler is incorporated in an assembly such as that shown in FIG. 1. Where such a stop is employed, it has proved desirable to configure the stop in conformity with the curved profile to which the reed would deflect if the reed deflected in a curve of a beam loaded by its own weight. This configuration is discussed in the previously identified Bailey patent, the pertinent disclo sure of which is hereby incorporated by reference. Generally, the maximum distance of the reed stop from the free end of the reed required to permit the reed to open sufiiciently to accommodate the exhaust discharge is about 0.300 inches.

The reed stop 47 is fastened in position with the same alien screws 54 utilized to mount the reed, and the reed stop 47 overlies the reed 32 in a coextensive fashion. It will thus be appreciated, that where the tip of the reed is cutoff as in FIGS. 3-7, the reed stop may be similarly fashioned at its end portion. As may be seen in FIG. 5, the reed stop 47 need not, however, be shaped identically at its terminus to that of the reed. In any event, the reed stop 47 is relatively rigid so as not to be moved by vibrations of the reed 32.

It will, however, be appreciated that the provision of the continuous venting minor portion of the exhaust outlet 30 so as to obviate reed-floating problems may enable elimination of the reed stop 47. Acceptable venting of this type may be provided for in a variety of ways. For example, instead of a generally straight terminus reed such as that of FIGS. 3-6, a cutoff" tip reed 32 having a generally arcuate, partially circular terminus 32c such as that shown on FIGS. 7 and i0 may be employed. In this embodiment, the venting portion of the exhaust outlet 30 is again provided by the open area most remote from the anchored end of the reed. A reed stop 47 conforming to the configuration of the reed 37 and designed in the cantilever deflection curve as discussed above may also be employed.

As shown in FIG. 8, a reed 32 which, if solid, would completely cover the exhaust opening 30 may be employed. To provide the continuous venting desirable to avoid floating and flutter, this reed may be provided with a generally circular aperture 57 adjacent the end superposed over the exhaust outlet. Preferably this aperture 57 is generally concentric with the generally circular exhaust outlet 30 in the reed-closed posi tion.

Empirical study has indicated that an aperture 57 having a diameter of about seven-sixteenth inch (so that the continuously vented minor portion of the exhaust outlet 30 is about 0.15 inches) produces desirable results. Such a reed 32 compared favorably from a power increase with the reed 32 discussed in connection with FIG. 6, and from a noise level standpoint the FIG. 8 reed appeared to be quieter. It is believed that this may be attributable to the superposed circular flow paths defined by the outlet opening 30 and the reed aperture 57.

The total reed length l and the cantilever length c (See FIG. Ill) were about 2% inches and 2 inches respectively for the studied reed. The remaining reed characteristics and other properties and dimensions were the same as in the case of the FIG. 6 example, with the exception of the use ofa reed stop 47 designed with the previously discussed cantilever deflection curvature for the particular reed dimensions.

It is also possible to provide for the continuous venting that is desirable through utilization of a reed 32 identical to that of FIG. 9 except for the absence of the aperture 56 (i.e., a reed the same as disclosed in the aforementioned Bailey patent) in combination with a generally circular exhaust opening 30 that has a generally cloverlea.f" type or scalloped outer periphery configuration. This general type muffler embodiment is illustrated in FIG. 9 with the reed 32 being shown as having a generally reduced end instead of having continuously straight lateral edges. The continuous venting would in this instance be provided by the curved, scalloped portions 57b of the generally annular exhaust outlet 30 that remain partially exposed even when the reed 32 is in a closed position. A properly configured reed stop 4'7, as discussed above, may also be utilized.

In FIG. 12 the continuous venting is shown as being provided in connection with a radiused tip solid reed 32 substantially similar to that of Fig. 11 (except for the fact that no reed aperture is provided) and an exhaust outlet 300 of generally trapezoidal shape. The forward corners 30d of the exhaust outlet on opposite sides of the tip of the reed 32 define together with the arcuate reed tip 3241, the venting flow paths. It will be appreciated that a generally triangular or other polygonal exhaust outlet may be employed with a similar venting effect at corners of the polygon. Preferably, the forward part of the polygonal exhaust outlet will be generally perpendicular to the longitudinal extent of the reed, and the corners" will be slightly rounded.

Testing of a reed muffler with a similar relationship of the reed to the exhaust outlet, i.e., with venting at the unblocked corners," indicated that a 7 percent power increase, as compared with a completely blocked outlet, may be obtained. It is expected that a similar minimization of power loss may be accomplished with the FIG. 12 arrangement.

A reed having a width w of about 1 /2 inches and a cantilever length of about 2 inches, in connection with a regular, generally trapezoidal outlet opening 300 having base dimensions b and c of about L620 inches and 0.880 inches respectively, as well as a height h of about 0.880 inches, is contemplated. With the reed width being in the range of about 70 to 80 percent of the length and with venting at corners" of the polygonal exhaust opening adjacent the edge generally perpendicular to the reed, it is believed that desirable results may be obtained.

Through continued reference to FIG. 12, it may be seen that only two securing screws 541 are shown. A similar arrangement may be employed in the various other embodiments illustrated. Also shown is a reed helper 63 that may, if desired, be secured over the reed by these same screws 54. The reed helper 63, which freely overlies but is not attached to the reed, may be of a material similar to the reed 32 and may have a similar thickness.

Generally the reed helper may be a plate, coextensive with the reed along a given length thereof to serve to avoid, during reed flexing, abrupt stresses on the reed at the cantilever anchor. The double thickness of materials provided by the plate generates a transition zone during such flexing.

Although a reed stop is not illustrated in FIG. 12, it may be employed if desired. Also, a spark arrestor suitably conforming to the outlet opening 300 may be utilized.

It should be here noted that apart from the various reeds, exhaust outlets and reed stops heretofore discussed, the remaining muffler components (i.e., the housing 27 etc.) of these embodiments and their dimensions, may be identical to those of FIgS. 4i and 5 and the illustrated mufflers may be similarly utilized with the chain saw of FIGS. 1 and 2 in place of the illustrated mufflers 2 3.

With reference again to the mufflers featured in FIGS. 4 and 5, it may be seen that the particular embodiments therein described are additionally advantageous from the standpoint of removability of a spark arrestor 58. The spark arrestor 58 is provided by a generally cup-shaped screen seated on the bottom of the interior of the muffler housing 27 and projecting upwardly to a position generally coextensive with the flat surface as on which the reed 32 is mounted. The arrestor 5% may be suitably fastened to the housing 27 as indicated at 60 in FIG. 4, or to the baffle 560 as indicated at 61 in FIG. 5.

With the embodiments in FIGS. 4 and 5, i.e., with the generally straight reed terminus and with a stop at least not projecting beyond the reed (See FIG. 4), replacement of the spark arrestor 58 without removing the reed 32 is facilitated in the following manner. A suitable tool, such as an allen wrench or the like, may be utilized to flex the reed toward its most deflected configuration. With the reed thus deflected, the spark arrestor may be removed (after removing the fastening means 60 with a screwdriver or the like), by generally pivoting the arrestor toward the outer portion of the muffler. A new replacement arrestor may be inserted by simply reversing the procedure.

As will be apparent from the foregoing, the illustrated embodiments of mufflers of the present invention each provide for the continuous venting of exhaust gas through a flow path bounded by a periphery curved in a plane transverse to the direction of exhaust gas flow through the exhaust outlet. In the embodiments of FIGS. 4-7 and 9 this curved boundary is provided by generally circular exhaust outlet 30. In FIG. 9 a compound curved boundary is provided by the scalloped portions 57b of that generally circular outlet 30. In the FIG. 3 embodiment, the curved boundary is provided by the reed opening 56, while in FIG. 12, the curved boundary is provided, in part by the arcuate reed tip 32d.

It will thus be seen that according to the present invention a muffler employing a cantilevered reed valve extending over an exhaust opening, and minimizing problems offlutter and floating has been provided.

Of added significance is the utilization of a generally flat reed supported on a generally flat surface through which an exhaust opening of the muffler is provided. With this arrange ment, problems that might be encountered with poor standoff characteristics, that might reduce muffler efiiciency, may be avoided without the need for undesirably increasing the spring force of the reed valve.

Also of significance is the fact that the inlet and exhaust outlet of the mufiler may be operationally offset from one another to avoid direct exhaust impulse on the reed during continuous venting.

Additional advantages are provided where the straight terminus-type reed is utilized thus enabling spark arrestor replacement and installation in an easy manner. The provision of an aperture in the reed end is also advantageous from a noise level standpoint.

Although the invention has been described with reference to particular preferred embodiments, it will be appreciated by those skilled in the art that additions, substitutions, modifications and deletions may be made without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

l. A muffler for an internal combustion engine comprising:

a housing defining an exhaust gas flow path for communicating with an exhaust port of the engine and an exhaust outlet opening for communicating with the surrounding atmosphere, said outlet opening having an area in the range of about 0.25 to 1.25 square inches;

a flexible, elongate, reed spring;

attaching means for fixedly anchoring said elongate reed spring adjacent one end thereof with said reed supported in cantilever fashion externally of said housing and with the other end thereof normally blocking, in a reed-closed position, a portion of the area of said outlet opening in the range of about 55 percent to about percent, the remainder of the area of said outlet opening providing continuous communication between said exhaust gas flow path and the atmosphere surrounding aid housing;

said reed being deflectable to a reed open position in response to exhaust gases passing through said exhaust outlet opening.

2. The muffler according to claim 1 wherein:

said other end of said reed is provided with at least one aperture disposed over said exhaust outlet opening; and wherein said remainder of the area of said exhaust outlet opening communicates with the atmosphere through said reed aperture.

3. The muffler according to claim 2 wherein:

said exhaust outlet opening and said at least one reed aperture are generally circular and generally concentric with said reed in a reed-closed position.

4. The muffler according to claim 1 wherein:

said exhaust outlet opening is defined by a scalloped periphery; and wherein said remainder of the area of said exhaust outlet opening is defined between a portion of said scalloped periphery and a portion of the edges of said reed spring.

5. The muffler according to claim 1 wherein:

said other end of said reed spring is provided with a generally straight edge extending generally transversely of the longitudinal extent of said reed spring; and wherein said remainder of the area of said exhaust outlet opening is defined between the periphery of said exhaust outlet opening and said generally straight edge.

6. The muffler according to claim 5 wherein:

said generally straight edge is inclined with respect to the longitudinal extent of said reed spring.

7. The muffler according to claim 5 further comprising:

a cup-shaped spark arrestor seated in said exhaust outlet.

8. The muffler according to claim 1 wherein said reed is provided with a generally arcuate tip, and wherein said outlet opening is polygonal;

said remainder of the area of said outlet opening being defined by said arcuate tip on opposite sides of the reed at the forward end of said exhaust outlet opening.

9. in combination with an internal combustion engine having a displacement in the range of about 2 to 8 cubic inches and including an exhaust port, a muffler comprising:

a housing defining an expansion chamber having a volume in the range of about 2 to 40 cubic inches;

said expansion chamber defining an exhaust inlet communicating with said exhaust port of said engine and an exhaust outlet opening communicating with the surrounding atmosphere;

said exhaust outlet opening having an area in the range of about 0.25 to 1.25 square inches;

a flexible, elongate, reed spring;

attaching means for fixedly anchoring said elongate reed spring adjacent one end thereof with said reed spring supported in cantilever fashion externally of said housing and with the other end thereof normally blocking in a reed closed position, a portion of the area of said exhaust outlet opening in the range of about 55 percent to about 85 percent, the remainder of the area of said outlet opening providing continuous communication between said expansion chamber and the atmosphere surrounding said housing;

said reed spring being deflectable to a reed open position in response to the application of force in the range of about I to 10 pounds by exhaust gases passing through said exhaust outlet opening; and

the exhaust being provided in a pressure range of about i to I an exhaust outlet opening to said generally flat outer surface and operationally displaced from alignment with said exhaust inlet; a flexible, elongate and generally flat spring reed; and cantilever support means for fixedly anchoring said reed to said housing adjacent one end of said reed with the major portion of said reed being normally supported, in a closed portion of said reed, on said generally flat outer surface and with the portion of said reed remote from said one end blocking a major portion of said exhaust outlet while a minor portion of said exhaust outlet is in continuous communication between said expansion chamber and the atmosphere surrounding said housing; said reed being deflectable to an open position by the force of exhaust gases passing through said exhaust outlet and acting on said reed to deflect said reed about said support means; and said minor portion of said exhaust outlet being of a magnitude to continuously vent an amount of exhaust gas sufficient to avoid substantial flutter of said reed during en gine idle and to avoid substantialfloating of said reed during engine operation. 11. A muffler for an internal combustion engine comprising: a rigid housing defining an expansion chamber and having at least one generally flat, planar outer surface, said expansion chamber including: an exhaust inlet for communicating with an exhaust port of the engine, and an exhaust outlet opening to said generally flat outer surface and operationally displaced from alignment with said exhaust inlet; a flexible, elongate and generally flat spring reed having a length dimension greater than its width dimension; and cantilever support means for fixedly anchoring said reed to said housing adjacent one end of said reed with the major portion of said reed being normally supported, in a closed position of said reed, on said generally flat outer surface and with the portion of said reed longitudinally remote from said one end blocking a major portion of said exhaust outlet while a minor portion of said exhaust provides continuous communication between said expansion chamber and the atmosphere surrounding said housing; said reed being deflectable to an open position by the force of exhaust gases passing through said exhaust outlet and acting on said reed to deflect said reed about said cantilever support means; and said minor portion of said exhaust outlet being of a magnitude to continuously vent an amount of exhaust gas sufficient to avoid substantial flutter of said reed during engine idle and to avoid substantial floating of said reed during engine operation. 12. A muffler for an internal combustion engine comprising; a housing defining an exhaust gas flow path having an exhaust inlet for communicating with an exhaust port of the engine and an exhaust outlet for communicating with the surrounding atmosphere, said exhaust inlet and said exhaust outlet being operationally displaced from alignment with one another so that said exhaust gas flow path is tortuously defined; a flexible, elongate and generally flat spring reed having a length dimension greater than its width dimension; support means including anchor means fixedly anchoring said reed adjacent one longitudinal end thereof and including a generally flat planar support surface for normally supporting a major portion of said reed in a closed reed position; the end portion of said reed longitudinally remote from said one end blocking a major portion of said exhaust outlet while a minor portion of said exhaust outlet provides continuous communication between said exhaust gas flow path and the surrounding atmosphere; said reed being deflectable to an open position by the force of exhaust gases passing through said exhaust outlet and acting on said reed to deflect said reed about said anchor means; and

said minor portion of said exhaust outlet being of a magnitude to continuously vent an amount of exhaust gas sufficient to avoid substantial flutter of said reed during engine idle and to avoid substantial floating of said reed during engine operation.

13. A muffler for an internal combustion engine comprising: a housing defining an exhaust gas flow path having an exhaust inlet for communicating with an exhaust port of the engine and an exhaust outlet communicating with the surrounding atmosphere;

a flexible elongate reed spring; means for fixedly anchoring said reed spring adjacent one reed spring end, with the end portion of said reed spring remote from said one end blocking, in a reed-closed position, a major portion of said exhaust outlet, while a minor portion of said exhaust outlet remains in continuous communication with the surrounding atmosphere through a venting flow path bounded by at least one of said reed spring and said exhaust outlet;

said venting flow path being at least partially bounded by a 2 generally curved peripheral boundary;

said reed being deflectable to an open position by the force of exhaust gases passing through said exhaust outlet and acting on said reed to deflect said reed about said one end thereof;

said minor portion of said exhaust outlet being of a magnitude to continuously vent an amount of exhaust gas sufflcient to avoid substantial flutter of said reed during engine idle and to avoid substantial floating of said reed during engine operation.

14. The muffler according to claim 13 wherein: said generally curved peripheral boundary is provided by an aperture in said remote end of said reed spring.

15. The mufller according to claim 14 wherein: said aperture and said exhaust outlet are each generally circular and generally axially aligned.

16. The muffler according to claim 13 wherein: said curved peripheral boundary is provided at least in part by said exhaust outlet, said exhaust outlet being generally a generally arcuate end, and wherein:

said generally curved peripheral boundary is defined in part by said arcuate end of said reed. 20. The muffler according to claim 13 in combination with said internal combustion engine and a chain saw assembly on which said muffler and said engine are mounted, and wherein:

said chain saw assembly includes a generally planar guide bar extending longitudinally at one end thereof;

said exhaust outlet of said muffler being generally circular and oriented in a direction generally normal to the plane of said guide bar;

said venting flow path being in part defined by said generally circular exhaust outlet and a generally straight terminus of said reed spring inclined with respect to the longitudinal extent of said reed spring.

21. A method of muffling the exhaust of an internal combustion engine passing into a muffler housing having an exhaust outlet opening cooperating with a cantilever supported reed spring, the method comprising:

with the engine at idle condition, venting gas from the muffler housing through a minor portion of the exhaust outlet opening with the reed in a reed-closed position to prevent substantialflutter of the reed; and with the engine at operatlng condition, continuing to vent exhaust through said minor portion of said exhaust outlet to prevent substantial floating of the reed.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 759 Dated February 22, 1972 Inven tor(s) J Bailey It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4, line 54 change "2" to --3-- Col. 4, line 59, change "2" to --3-- Col. 8, line 50, change "37" to --32---- C01. 8, line 65, before "inches" insert "square-- C01. 9, line 6, change "56" to --57-'- C01. 10, line 31, change "56" to --57-- Signed and sealed this 25th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting; Officer Commissioner of Patents FORM PO-105O (10-69) USCOMM-DC 0O376-P69 u.s. covnmuur runmuc orncz any o-un-au UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 759 Dated q y 1972 Jay R. Bailey Inven tor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col, 4, line 54 changeT'Z" to -3- 1 Col. 4, line 59, change "2 to -3 C01. 10, line 31, change "56" to "57-- Signed and sealed this 25th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-IOSO (10-69) USCOMM-DC 60376-P69 h u.s. covtnnunrr rrmnmc orrlrt G969 0:66-:J4 

1. A muffler for an internal combustion engine comprising: a housing defining an exhaust gas flow path for communicating with an exhaust port of the engine and an exhaust outlet opening for communicating with the surrounding atmosphere, said outlet opening having an area in the range of about 0.25 to 1.25 square inches; a flexible, elongate, reed spring; attaching means for fixedly anchoring said elongate reed spring adjacent one end thereof with said reed supported in cantilever fashion externally of said housing and with the other end thereof normally blocking, in a reed-closed position, a portion of the area of said outlet opening in the range of about 55 percent to about 85 percent, the remainder of the area of said outlet opening providing continuous communication between said exhaust gas flow path and the atmosphere surrounding aid housing; said reed being deflectable to a reed open position in response to exhaust gases passing through said exhaust outlet opening.
 2. The muffler according to claim 1 wherein: said other end of said reed is provided with at least one aperture disposed over said exhaust outlet opening; and wherein said remainder of the area of said exhaust outlet opening communicates with the atmosphere through said reed aperture.
 3. The muffler according to claim 2 wherein: said exhaust outlet opening and said at least one reed aperture are generally circular and generally concentric with said reed in a reed-closed position.
 4. The muffler according to claim 1 wherein: said exhaust outlet opening is defined by a scalloped periphery; and wherein said remainder of the area of said exhaust outlet opening is defined between a portion of said scalloped periphery and a portion of the edges of said reed spring.
 5. The muffler according to claim 1 wherein: said other end of said reed spring is provided with a generally straight edge extending generally transversely of the longitudinal extent of said reed spring; and wherein said remainder oF the area of said exhaust outlet opening is defined between the periphery of said exhaust outlet opening and said generally straight edge.
 6. The muffler according to claim 5 wherein: said generally straight edge is inclined with respect to the longitudinal extent of said reed spring.
 7. The muffler according to claim 5 further comprising: a cup-shaped spark arrestor seated in said exhaust outlet.
 8. The muffler according to claim 1 wherein said reed is provided with a generally arcuate tip, and wherein said outlet opening is polygonal; said remainder of the area of said outlet opening being defined by said arcuate tip on opposite sides of the reed at the forward end of said exhaust outlet opening.
 9. In combination with an internal combustion engine having a displacement in the range of about 2 to 8 cubic inches and including an exhaust port, a muffler comprising: a housing defining an expansion chamber having a volume in the range of about 2 to 40 cubic inches; said expansion chamber defining an exhaust inlet communicating with said exhaust port of said engine and an exhaust outlet opening communicating with the surrounding atmosphere; said exhaust outlet opening having an area in the range of about 0.25 to 1.25 square inches; a flexible, elongate, reed spring; attaching means for fixedly anchoring said elongate reed spring adjacent one end thereof with said reed spring supported in cantilever fashion externally of said housing and with the other end thereof normally blocking in a reed closed position, a portion of the area of said exhaust outlet opening in the range of about 55 percent to about 85 percent, the remainder of the area of said outlet opening providing continuous communication between said expansion chamber and the atmosphere surrounding said housing; said reed spring being deflectable to a reed open position in response to the application of force in the range of about 1 to 10 pounds by exhaust gases passing through said exhaust outlet opening; and the exhaust being provided in a pressure range of about 1 to 10 p.s.i.
 10. In combination with a chain saw driven by an internal combustion engine, a muffler mounted on said chain saw and comprising: a rigid housing defining an expansion chamber and having at least one generally flat, planar outer surface, said expansion chamber including: an exhaust inlet for communicating with an exhaust port of the engine, and an exhaust outlet opening to said generally flat outer surface and operationally displaced from alignment with said exhaust inlet; a flexible, elongate and generally flat spring reed; and cantilever support means for fixedly anchoring said reed to said housing adjacent one end of said reed with the major portion of said reed being normally supported, in a closed portion of said reed, on said generally flat outer surface and with the portion of said reed remote from said one end blocking a major portion of said exhaust outlet while a minor portion of said exhaust outlet is in continuous communication between said expansion chamber and the atmosphere surrounding said housing; said reed being deflectable to an open position by the force of exhaust gases passing through said exhaust outlet and acting on said reed to deflect said reed about said support means; and said minor portion of said exhaust outlet being of a magnitude to continuously vent an amount of exhaust gas sufficient to avoid substantial flutter of said reed during engine idle and to avoid substantial floating of said reed during engine operation.
 11. A muffler for an internal combustion engine comprising: a rigid housing defining an expansion chamber and having at least one generally flat, planar outer surface, said expansion chamber including: an exhaust inlet for communicating with an exhaust port of the engine, and an exhaust outlet opening to said generally flat outer surface and operationally displaced from alignment with said exhaust inlet; a flexible, elongate and generally flat spring reed having a length dimension greater than its width dimension; and cantilever support means for fixedly anchoring said reed to said housing adjacent one end of said reed with the major portion of said reed being normally supported, in a closed position of said reed, on said generally flat outer surface and with the portion of said reed longitudinally remote from said one end blocking a major portion of said exhaust outlet while a minor portion of said exhaust provides continuous communication between said expansion chamber and the atmosphere surrounding said housing; said reed being deflectable to an open position by the force of exhaust gases passing through said exhaust outlet and acting on said reed to deflect said reed about said cantilever support means; and said minor portion of said exhaust outlet being of a magnitude to continuously vent an amount of exhaust gas sufficient to avoid substantial flutter of said reed during engine idle and to avoid substantial floating of said reed during engine operation.
 12. A muffler for an internal combustion engine comprising: a housing defining an exhaust gas flow path having an exhaust inlet for communicating with an exhaust port of the engine and an exhaust outlet for communicating with the surrounding atmosphere, said exhaust inlet and said exhaust outlet being operationally displaced from alignment with one another so that said exhaust gas flow path is tortuously defined; a flexible, elongate and generally flat spring reed having a length dimension greater than its width dimension; support means including anchor means fixedly anchoring said reed adjacent one longitudinal end thereof and including a generally flat planar support surface for normally supporting a major portion of said reed in a closed reed position; the end portion of said reed longitudinally remote from said one end blocking a major portion of said exhaust outlet while a minor portion of said exhaust outlet provides continuous communication between said exhaust gas flow path and the surrounding atmosphere; said reed being deflectable to an open position by the force of exhaust gases passing through said exhaust outlet and acting on said reed to deflect said reed about said anchor means; and said minor portion of said exhaust outlet being of a magnitude to continuously vent an amount of exhaust gas sufficient to avoid substantial flutter of said reed during engine idle and to avoid substantial floating of said reed during engine operation.
 13. A muffler for an internal combustion engine comprising: a housing defining an exhaust gas flow path having an exhaust inlet for communicating with an exhaust port of the engine and an exhaust outlet communicating with the surrounding atmosphere; a flexible elongate reed spring; means for fixedly anchoring said reed spring adjacent one reed spring end, with the end portion of said reed spring remote from said one end blocking, in a reed-closed position, a major portion of said exhaust outlet, while a minor portion of said exhaust outlet remains in continuous communication with the surrounding atmosphere through a venting flow path bounded by at least one of said reed spring and said exhaust outlet; said venting flow path being at least partially bounded by a generally curved peripheral boundary; said reed being deflectable to an open position by the force of exhaust gases passing through said exhaust outlet and acting on said reed to deflect said reed about said one end thereof; said minor portion of said exhaust outlet being of a magnitude to continuously vent an amount of exhaust gas sufficient to avoid substantial flutter of said reed during engine idle and to avoid substantial floating of said reed during engine operation.
 14. The muffler according to claim 13 wherein: said geNerally curved peripheral boundary is provided by an aperture in said remote end of said reed spring.
 15. The muffler according to claim 14 wherein: said aperture and said exhaust outlet are each generally circular and generally axially aligned.
 16. The muffler according to claim 13 wherein: said curved peripheral boundary is provided at least in part by said exhaust outlet, said exhaust outlet being generally circular.
 17. The muffler according to claim 16 wherein: said venting flow path is bounded in part by a generally straight terminus of said reed spring, the muffler further comprising: a cup-shaped spark arrestor seated in said generally circular exhaust outlet and extending into said housing.
 18. The muffler according to claim 13 wherein: said exhaust outlet is generally circular and provides said curved peripheral boundary by a scalloped periphery of said exhaust outlet.
 19. The muffler according to claim 13 wherein said reed has a generally arcuate end, and wherein: said generally curved peripheral boundary is defined in part by said arcuate end of said reed.
 20. The muffler according to claim 13 in combination with said internal combustion engine and a chain saw assembly on which said muffler and said engine are mounted, and wherein: said chain saw assembly includes a generally planar guide bar extending longitudinally at one end thereof; said exhaust outlet of said muffler being generally circular and oriented in a direction generally normal to the plane of said guide bar; said venting flow path being in part defined by said generally circular exhaust outlet and a generally straight terminus of said reed spring inclined with respect to the longitudinal extent of said reed spring.
 21. A method of muffling the exhaust of an internal combustion engine passing into a muffler housing having an exhaust outlet opening cooperating with a cantilever supported reed spring, the method comprising: with the engine at idle condition, venting gas from the muffler housing through a minor portion of the exhaust outlet opening with the reed in a reed-closed position to prevent substantial flutter of the reed; and with the engine at operating condition, continuing to vent exhaust through said minor portion of said exhaust outlet to prevent substantial floating of the reed. 